1. Field of the Invention
The present invention relates to an ink jet printing apparatus provided with a heat application treatment unit that gives heat treatment to a medium having ink jet prints formed on it.
2. Related Background Art
Conventionally, as a printing medium having a thermoplastic layer on the printing side, there has been known the medium which is provided with a porous polymeric layer formed on the printing surface thereof (such as disclosed in Japanese Patent Laid-Open Application No. 7-237348). The porous polymeric layer becomes the transparent polymeric film that protects the printed surface when thermally treated. Also, in accordance with Japanese Patent Laid-Open Application No. 8-2090, there is disclosed a printing medium having a resin porous layer formed on the printing surface thereof. The resin porous layer becomes the transparent resin film that protects the printed surface when thermally treated.
When a heat treatment is given to the ink droplets discharged onto the porous polymeric layer of a printing medium after the ink droplets have been permeated into the ink retention layer formed under the porous polymeric layer, a considerable amount of water vapor is generated due to the evaporation of the moisture contained in them as a large amount of heat and ink solvent. A phenomenon of the kind is not necessarily confined only to the case of the printing medium described above. This phenomenon also takes place when the heating fixation is performed after the ink jet printing is made on an ordinary paper sheet.
The heat which is generated by the heating fixation after an ink jet printing is executed produces an unfavorable effect on the ink jet printing head and other in the printing unit installed in the apparatus main body or on the printing medium if it is stored in the interior of the apparatus main body. For example, there is a problem that the discharge openings of an ink jet printing head of may be clogged due to dried liquid of ink in the discharge openings or the printing medium may be deformed in the printing medium storage provided in the interior of the apparatus.
Particularly, if a structure is arranged so that the heating fixation unit is installed on the lower part of an ink jet printing unit for the purpose of maintaining the printing apparatus in a smaller size, the heat generated on the lower part of the apparatus is allowed to be transferred upward, thus affecting the ink jet printing unit arranged above the heating fixation unit, among some other problems encountered as described above.
Further, if a printing medium stored in the apparatus is a rolled paper, it is curled more easily. Then, when such curled paper sheet is used for ink jet printing, there is a problem that the printing medium tends to be in contact with the ink jet printing head.
Further, if the printing medium stored in the apparatus is the one which is provided with porous polymeric layer on the printing surface thereof, there is a problem that the porous property of the medium may be deteriorated by heat in some cases.
Furthermore, there is a problem that the water vapor generated in the heating fixation unit by the evaporation of moisture contained in the solvent of ink produces unfavorable effect on the ink jet printing head and printing medium as well.